The present invention generally relates to a method for mitigating the formation of T-tops and/or upper surface stringers and/or crusts in a photoresist.
In the semiconductor industry, there is a continuing trend toward higher device densities. Fabrication of very large scale integrated circuits (VLSI) and ultra large scale integrated circuits (ULSI) requires that resist materials, lithographic processes, and exposure tools meet necessary performance demands for high throughput manufacturing of sub-micron feature size devices. In particular, the semiconductor industry is producing with increasing frequency integrated circuits having structures which are markedly less than 1 xcexcm. The increased integration density increases the requirements imposed on the photolithographic process.
For exposure apparatuses using short-wavelength light such as an excimer laser, chemical amplification type photoresists are often employed. The chemical amplification type photoresist generally consists of a resin, a photosensitive acid generator, and a solubilizer or a cross-linking agent. The acid generator generates an acid upon exposure. During post exposure baking (PEB), this acid functions as a catalyst to encourage the reaction of the solubilizer or the cross-linking agent, and a pattern is formed by development. A photoresist using the solubilizer forms positive patterns, and a photoresist using the cross-linking agent forms negative patterns.
Unfortunately, the chemical amplification type photoresist lacks stability, although it is superior in resolution, since in PEB the catalytic action of an acid generated by exposure is difficult to control. Especially in the case of positive photoresist, if a basic gas such as ammonia gas or amine gas is present in the atmosphere between an exposure apparatus and a PEB apparatus, an acid generated by exposure reacts with this basic gas and is neutralized. Consequently, a portion which is supposed to dissolve in a developer become difficult to dissolve (e.g., a so-called hard dissolution phenomenon takes place). If this hard dissolution layer is formed, a so-called T-top phenomenon occurs in which a pattern formed by development is given a T-shape having an overhang in the upper portion. FIG. 1a schematically illustrates a structure 10 including a photoresist layer 18 over an underlayer 20 (e.g., metal layer, nitride layer, polysilicon layer), which lies over a substrate 22. FIG. 1b illustrates the structure 10 after being exposed. The photoresist layer 18 includes exposed portions 28, which are intended to be dissolved. The exposed portions include hard to dissolve portions 30 which may lead to T-tops and/or stringers and/or crusts. FIG. 1c. Illustrates the structure 10 after a development process was performed thereon. As a result of the hard-dissolution problem, the developed photoresist layer 18 includes T-tops 32 and upper surface stringers 34. The T-tops 32 are the result of a sparingly soluble skin which results in a T-profile of the resist edges after development. T-topping, stringers and crusts interfere with inspection of line width and/or line spacing, and in a subsequent dry etching process affect the dimensionally faithful transfer of the dimensions of the resist structures into the underlayer 20.
In view of the above, it would be desirable to have a method to eliminate or mitigate the presence of T-tops and/or upper surface stringers and/or crusts.
The present invention provides for a method which eliminates or mitigates the presence of T-tops and/or upper surface stringers and/or crusts. After a photoresist layer has been exposed, a chemical mechanical polishing (CMP) process is performed on the photoresist layer to remove portions of the photoresist that might result in T-tops and/or upper surface stringers and/or crusts in the photoresist layer after development. After the CMP process is complete, the photoresist layer is employed as an etch mask for the underlying layer (e.g., polysilicon layer, metal layer, silicon nitride layer, or oxide layer). The elimination or mitigation of the T-tops and/or upper surface stringers and/or crusts from the photoresist layer via the CMP process substantially facilitates proper transfer of features of the photoresist layer to the underlayer.
One particular aspect of the present invention relates to a method for mitigating formation of T-tops and/or stringers from a structure. A photoresist layer of the structure is developedxe2x80x94the structure includes an underlayer under the photoresist layer, and a substrate under the underlayer. A chemical mechanical polishing process is performed to remove a portion of the photoresist layer, the portion including a difficult to dissolve which might lead to the formation of at least one of a T-top and/or a stringer.
Another aspect of the present invention relates to a method for mitigating formation of T-tops and/or stringers and/or crusts in a structure. A photoresist layer of the structure is exposed. The structure further includes an underlayer under the photoresist layer, and a substrate under the underlayer. A chemical mechanical polishing process is employed to remove a predetermined thickness of the photoresist layer. An underlayer etch is performed to remove select portions of the underlayer.
Another aspect of the present invention relates to a method for mitigating formation of T-tops and/or stringers and/or crusts in a structure. A photoresist layer of the structure is exposed, the structure further includes an underlayer under the photoresist layer, and a substrate under the underlayer. A means to remove a predetermined thickness of the photoresist layer is employed. An underlayer etch is performed to remove select portions of the underlayer.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.